Class 9 Science Chapter 11 Sound
1. How does the sound produced by
a vibrating object in a medium
reach your ear?
Answer: When an object vibrates, it forces the neighbouring particles of the medium to vibrate. These vibrating particles then force the particles adjacent to them to vibrate. In this way vibrations produced by an object are transferred till it reaches the ear.
2. Explain how sound is produced
by your school bell.
Answer : When the school bell is struck with a hammer, it starts vibrating and as a result of these vibrations, sound waves are produced in air.
3. Why are sound waves called
mechanical waves?
Answer : Sound waves are mechanical waves because they need a material medium for propagation, like air or liquids like water, or metals like silver.
4. Suppose you and your friend are
on the moon. Will you be able to
hear any sound produced by
your friend?
Answer : No, because sound waves need a medium through which they can propagate. Since there is no material medium on the moon due to the absence of atmosphere, you cannot hear any sound on the moon.
5. Which wave property determines
(a) loudness, (b) pitch?
Answer : (a) The loudness of sound is determined by the amplitude of sound waves.
(b) The pitch of sound is determined by the frequency of vibration of the sound producing source.6. Guess which sound has a higher
pitch: guitar or car horn?
Answer : Guitar has a higher pitch than car horn because sound produced by the strings of guitar has high frequency than that of car horn. High the frequency higher is the pitch.
7. What are wavelength, frequency,
time period and amplitude of a
sound wave?
Answer : Wavelength: The distance between two consecutive crests or troughs is known as the wavelength. Its SI unit is metre (m).
8. How are the wavelength and frequency of a sound wave related to its speed?
Answer : we know that ,speed=wavelength×frequency, so this means that speed is directly proportional to the wavelength and frequency ,so if any of them increase then the speed also increases.
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